1. Field of the Invention
The invention relates to a press molding die capable of preventing a workpiece from moving during press molding, and a manufacturing method of same.
2. Description of the Related Art
In order to press a workpiece into shapes, initially, the workpiece is placed on a molding surface of a molding die having a predetermined-shaped concave portion. On the periphery of the concave portion, the workpiece is pressed to the molding die by a pad and is fixed. Then, the workpiece is plastically deformed by being pressed by a punch having a shape corresponding to the concave portion. In such press molding, a problem occurs that the workpiece moves into the concave portion, that is, so-called displacement of the workpiece is caused. The displacement of the workpiece affects the accuracy of a press molded product, the quality of a surface of the press molded product, and the like. In addition, due to such a problem useful lives of the molding die and the punch are shortened, and the cost of maintenance of the molding die and the punch increases.
An example of methods for preventing the workpiece from moving is to increase the pressing force of the pad during press molding. However, since the pressing force of the pad acts in the direction perpendicular to the direction in which the workpiece moves, it is necessary to apply a tremendous amount of pressing force in order to prevent the workpiece from moving. Also, it is impossible to prevent the workpiece from moving substantially completely. It is also possible to prevent the workpiece from moving by precisely controlling the distance between the molding die and the pad. However, such control requires a complicated configuration of the die and skills in adjustment, thereby increasing the cost of manufacturing the die.
As related art, Japanese Patent Laid-Open Publication No. 3-268808 discloses a known metalworking tool for suppressing occurrence of a weld marks which are likely to occur during cold work and press work of metal, and for preventing a slip which occurs due to lubricating oil used for preventing occurrence of the weld marks. The metalworking tool is a plastic forming tool and a plurality of small dents is formed on the smooth surface of the metalworking tool. Each of the dents has a diameter of 5 to 50 μm, and a depth of 0.5 to 5 μm. The total area of the dents accounts for 5 to 50% of the surface area of the tool before the dents are formed.